This invention is concerned with improvements in low profile electronic type platform weighing systems. A first type system which has been used in the past employs a platform supported by several load cells whose outputs are averaged electrically to allow forces to be measured over a large area of the platform. The advantage of such a system is that the relative sensitivities of each load cell can be easily adjusted electrically, permitting the scale to have equal sensitivity irrespective of the location of the load on the platform. This adjustment is referred to in the trade as "corner sealing." The disadvantage of the multiple load cell system is that it necessarily results in de-rating of the individual load cells to protect them against high loads created by off-center application of the force to the platform. In the worst case, where the load is applied directly over one corner of a platform supported by a load cell at each of its four corners, mathematical analysis demonstrates that each scale must be capable of withstanding three-fourths of the total applied load, thereby decreasing the sensitivity of the system in a situation where the load is applied centrally on the platform with each of the load cells supporting only one quarter of the load. Thus, the potential accuracy of the multiple load cell system is reduced.
A second type of platform scale employs the well-known principles of flexures, pivots, levers and torque tubes to mechanically combine the forces applied to the platform, and thereby permits the measurement of forces with a single load cell which does not have to be derated as described above. Conventional lever systems employ pivots, bearings and knife edges which continuously wear and must be periodically filed, aligned and replaced. It is therefore inconvenient and costly to maintain and mechanically adjust the various lever arm lengths to achieve corner sealing and to maintain accuracy, and knife edge systems also introduce problems from lateral loading conditions.
These problems inherent in conventional lever systems are eliminated by replacing the pivots and bearings with ribbon-like beams of steel called flexures. Flexures, which are known in the art, have no moving parts and require no adjustment or maintenance. The load on the platform is transmitted to the lever system through the flexure.
It is the primary object of this invention to provide an improved platform weighing system which combines the advantages of both multiple load cell systems and flexure-based lever type force transferral systems employing single load cells, without incurring the disadvantages normally inherent in either of such systems. It is a further object to provide an improved flexure element which can be readily modified to change its sensitivity, and which is useful either as a flexure element in a platform weighing system or as a transducer.